(1) Field of the Invention
This invention relates to novel pyrazole derivatives, method for preparation thereof, a selective herbicidal composition containing as an active ingredient one or more of said derivatives, and method for damaging and controlling weeds using said derivatives.
(2) Description of the Prior Art
Hitherto, some pyrazole derivatives having herbicidal activity have been known. For example, Japanese Patent Publication No. 36648/79 (corresponding to U.S. Pat. Nos. 4,063,925 and 4,146,726) and Japanese Laid-open Patent Publication No. 41872/79 (corresponding to U.S. Pat. No. 4,230,481), Japanese Laid-open Patent Publication No. Sho 56-61358 (61358/81), U.S. Pat. No. 4,557,753 and U.S. patent application Ser. No. 735,656 disclose certain 4-benzoyl derivatives of pyrazole which are useful for herbicides.
Among these pyrazole derivatives, however, two compounds represented by the formula below are used practically and commercially as an active ingredient of a herbicide for use in a paddy field as far as the present inventors' knowledge is concerned. ##STR2##
All the pyrazole derivatives disclosed by the above-mentioned publication No. 41872/79 have a lower alkyl group, specifically CH.sub.3 group, at 3-position of the pyrazole ring.
Also the majority of the pyrazole derivatives disclosed by the above-mentioned publication No. 36648/79 have a lower alkyl group at the 3-position of the pyrrazole ring and --OH, --SH, a salt thereof or an organic acid ester thereof at 5-position of said ring; among the pyrazole derivatives disclosed by said publication, only the compound of the following formula is exemplified as a pyrazole derivative having hydrogen atom at 3-position (i.e., unsubstituted at 3-position) of the pyrazole ring: ##STR3##
The compound C, however, is inferior to the commercialized compound A in herbicidal activity as is apparent from the biological test data given in the above-mentioned publication No. 36648/79.
Despite the fact that a number of pyrazole derivatives have been synthesized and the herbicidal activity thereof has been tested, there has not been found a pyrazole derivative which is unsubstituted at 3-position of the pyrazole ring and which exhibits herbicidal activity except the above-mentioned compound C.
This is because synthesis of pyrazole derivatives unsubstituted at 3-position has been very difficult while a pyrazole derivative substituted by an alkyl at 3-position has been relatively readily prepared, and because the former compound has been believed to be less active in herbicidal action and thus less practical than the latter one.
The present inventors have done intensive research on pyrazole derivatives having hydrogen atom at 3-position of the pyrazole ring and have unexpectedly found that some of these pyrazole derivatives exhibit herbicidal action against a wide range of weeds, particularly against perennial weeds such as perennial flat sedge (Cyperus serotinus), bulrush (Scirpus juncoides) and perennial spikerush (Eleocharis kuroguwai) which have been difficult to control and against which no useful herbicide has been developed. Moreover, the present inventors have found a process for readily preparing such 3-H pyrazole derivatives to complete the present invention. The 3-H pyrazole derivatives have no phytotoxicity upon a paddy-rice plant and, thus, can be used with safety.
The present inventors have filed an application for an invention on the basis of the above-mentioned knowledge and have been granted a patent thereto under the U.S. Pat. No 4,557,753,. In this U.S. Pat. No. 4,557,753, the pyrazole derivatives have hydrogen atom at 3-position of pyrazole ring, CH.sub.3 group at 1-position thereof and a specific substituent group at 5-position thereof.
After the present inventors have intensively advanced the researches, they have found that in the above-mentioned 3-H pyrazole derivatives, when 1-C.sub.2 H.sub.5 compounds having an ethyl group at 1-position of pyrazole ring and 1-CH.sub.3 compounds having methyl group at the same position are compared, 1-C.sub.2 H.sub.5 compounds showed remarkable effectiveness against to the grass weeds, and the improvement of the effectiveness against to the paddy weeds as Monochoria vaginalis, Alisma canaliculatum has reached to more than ten times as the effects of 1-CH.sub.3 compounds, which has been way above the initial expectation.
Among the compounds according to the present invention, there exist some compounds which show superior safety to cultivated plants, e.g., rice (Oryza satva), or show very high safety to corn (Zea mays) in the dry field farming, while some compounds show remarkable improvement of the effectiveness against to grass weeds in the field of corn (Zea mays), yellow nutsedges (Cyperus esculeutus) and broadleaf-weeds in comparison with that of 1-CH.sub.3 compounds.
Moreover, in comparison with prior art compound, the specificity of substitution at 1-position of prazole ring which is the features of the present invention is summed up as follows:
Firstly, in case of 3-CH.sub.3 type pyrazoles as recognized in the earlier patent application, U.S. Pat. No. 4,063,925, and as apparent from the comparison between the compounds of said U.S. Pat. No. 4,063,925: Compounds No. 44 and No. 11, Compounds No. 107 and No. 51, Compounds No. 108 and No. 14, and Compounds No. 109 and No. 105, it is clear that the intention of said U.S. Pat. No. 4,063,925 was directed to 1-CH.sub.3 compounds because there was no remarkable difference of activity between 1-CH.sub.3 type pyrazoles and pyrazoles substituted by alkyl group having more than two carbon atoms at 1-position (under the both conditions of paddy field and dry field farming).
On the other hand, in case of 3-H type pyrazoles, as shown in the later-described tables, there was remarkable difference of activity between 1-CH.sub.3 compounds and pyrazoles substituted by alkyl group having more than two carbon atoms at 1-position. In this aspect, it is understood that even a person skilled in the art could not expect the present invention.
Especially, under not only paddy-rice field conditions but also dry field farming, the present invention has such as inventive step that the present invention shows remarkable higher activity is not only soil treatment but also foliage application which show very high cultivated plant-selectivity. Furthermore, the present invention has sufficient inventive step in a point that it shows higher activity with respect to seriously harmful weeds such as grass weeds, broadleaf-weeds, etc., and further to Cyperus esculeutus, yellow nutsedge. Also, Japanese Laid-open Patent Publication No. Sho 56-61358 (61358/81), one of the prior arts, shows herbicidal activity of pyrazoles having methyl group at 3-position under the paddy-field conditions. In said Japanese Laid-open Patent Publication, the compound No. 4 has isopropyl group at 1-position. However, comparing with the compounds No. 2, No. 3 and No. 5, all having methyl group at 1-position, said compound No. 4 has lower activity. As aforementioned, in the 3-methyl type pyrazoles, the substituent of more than 1-C.sub.2 has no superior properties in comparison with 1-methyl compounds. Thus, it shows that the fact that in 3-H type pyrazoles, the superiority of having a substituent have more than C.sub.2 at 1-position instead of a methyl group could not be expected. At the same time, in said Japanese Laid-open Patent Publication, only applicability to the rice-field conditions was described. Therefore, the safety of the present compounds to economic plants, corn (Zea mays) included and applicability of the present compounds to the dry-field farming can not be expected from said Japanese Laid-open Patent Publication.